1. Technical Field
The present disclosure relates to electrosurgery. More particularly, the present disclosure relates to an automatic control circuit for an electrosurgical generator.
2. Background of Related Art
Surgeons typically try to regulate energy application by adjusting the basic power level of the electrosurgical generator and using the hand or foot switch to control the power applied over time. Unfortunately, that technique may lead to unintended power delivery or undesired duration of power delivery to the surgical site. Surgeons may also experience difficulty in repeatably and/or consistently desiccating tissue to the desired levels due to the limits of their human reaction time or machine response time when manual or foot activated switches are used for manual control. In addition, during endoscopic procedures, surgeons lose some visual and tactile indications of desiccation progression.
Calculations of feedback signals that are useful in the control of radio frequency (RF) electrosurgical instruments during operation can be summarized in two general forms. Analog computations tend to use expensive high frequency analog Root Mean Square (RMS) to direct current (DC) algorithms or circuits or less expensive Mean Absolute Deviation (MAD) circuits for computing the true, or near true in the case of MAD, RMS values of voltage and current which can be used to calculate power or impedance using Ohm's law. Additional methods are employed to calculate the load voltage to current phase angle in order to compensate for the reactive loading or the power factor (PF). Analog circuits typically have exponential responses or further filtering on PF and/or power which may result from a compromise between accuracy and response time. Calibration may also be difficult to maintain due to manufacturing and temperature variations.
Digital computations often mimic the analog implementation by computing the RMS values directly from digitized waveforms for voltage and current and then applying the phase angle or PF corrections. A circuit for automatically controlling the output of an electrosurgical generator utilizing digital computations is disclosed in U.S. Pat. No. 7,300,435 to Wham et al., assigned to Sherwood Services AG, the contents of which are hereby incorporated by reference in their entirety. U.S. Pat. No. 7,300,435 relates to an automatic control system that uses the phase difference between the voltage and current waveforms as calculated using a Goertzel algorithm to adjust the current, voltage or power delivered to the patient.